If you were in a car and traveling in a circle at constant speed, then you (and the car) would be accelerating towards the center of the circle. This acceleration is caused by an unbalanced or net force. At all points along the circular path, you would be heading in a direction which is tangent to the path. You would feel a strong inertial tendency to continue in motion in a direction tangent to the circle. The presence of an unbalanced force on your body pushes you towards the center of the circle so that you can make the turn rather than travel straight ahead. This force is supplied by the outside door, the seat belt and harness or friction between you and the seats. If this force were somehow removed, there would no longer be an unbalanced force on your body and you would fly out of the car and tangent to the circle. An object in motion would continue in motion in the same direction when not acted upon by an unbalanced force. That which is true of your motion in this car would be equally true of the motion of the eraser tied to the string (and not tied to the string).
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